As for stopping sex. You have every right to not have sex. At any time. This is no questions asked. So in the following discussion, please do not construe that I am advocating you continue to have sex, I am not, I'm evaluating the situation.
I'm approaching this wholistically to begin with.
Society and sex
The "sexual revolution" did a lot of good in helping to establish equality between the sexes, between sexual preferences and many issues surrounding sexuality. This statement is made with the caveat, that there is a long way to go, but this is coming from the state of the 1950s, it where so much was hidden or else a much larger group of people were branded and socially stigmatised than they are today.
One of the drawbacks of the morality surrounding sex is becoming looser, is that this has a tendency to be coupled with devaluing the intimate nature of it and the value of waiting. The pressure and expectation, in many cultures, for engaging in sexual intercourse are now quite low, as you say a few dates. This does make it difficult when trying to set a standard outside the norm.
For the sexual revolution to have really made headway, then people should not feel they have to have sex early in a relationship to be able to date. This is in many ways as bad as people being demonised for having sex before some societal constraint deems it to be ok (e.g. marriage).
Dating and sex
In terms of dating, per se, it is helpful to know why you are dating.
the alternatives (being alone or dating religious people) are not an option.
These do not sound like the most positive reasons for having sex early in a relationship. Although I'm sure that there's many, many people who do just that. Some good reasons to have sex are:
You want to.
You enjoy it.
To relieve sexual frustration.
You like the person and want to be close to them.
Some not so good reasons:
You feel obliged.
To gain something else from it.
So what are you expecting to get out of dating? To prevent loneliness, the company, the social aspect? Are you trying to find a long term partner?
If you are wanting a long term partner, there is no harm in waiting to have sex, as this may assist in weeding out potential partners. If someone doesn't want to hang around more than a few dates without sex, then they are more interested in having sex than getting to know you. So that's one easy fix in finding a suitable partner.
Now to get to your problem.
The issues with deciding to stop having sex
Step 1 - Monogamy
A 5 month relationship is not long in terms of knowing and making decisions about the future. The most basic and first step towards making a commitment is the agreement for monogamy. That is saying, I care about you and this relationship enough, that I am not needing or wanting to find this intimacy with anyone else, I only want it with you.
I don't want to end it but talking about getting serious hasn't been
By serious I mean being generally committed to each other, making an effort for a future together, not necessarily moving together or getting engaged instantly, but both agreeing that those things will happen at some point.
After 5 months, this is usually too early for most people. After 12 months, it's reasonable to apply pressure if it hasn't been brought up. It's helpful to play or tease at taking it to the next level. Usually this would begin with divulging each other's feelings. Saying "I love you", admitting that you're in love with the other person.
If this guy is right for you, then allowing the relationship to develop is important, in terms of evolving into a more committed relationship with discussions about the future.
having sex in this
uncertain stage this long is starting to affect my self-worth.
If the sexual relationship is eroding your self worth, then you need to ask yourself why. Are you feeling used? Is it something about your partner or is this to do with your conservative upbringing? It's vital for you to establish this. Because if it's your partner, then you need to also question whether he is right for you sex or no sex. Many relationships will continue out of convenience and the regular sex being a part of that convenience. So you are right to be concerned.
Will stopping sex help the relationship?
If someone truly loves you and wants you in their life, stopping sex should not cause you to lose them. I can say this from experience (in both directions). However, this is still early days and it takes time to develop trust and for him to really know what your motives are.
It will be difficult for your partner and this is something that you'll both need to navigate. Acknowledge it will be difficult. Explain how it's affecting your self worth. This is a huge issue for you. Explain your background to him, as you have done with us.
how do I say that in a productive way and not seem manipulative?
You cannot stop your partner from feeling like you're giving him an ultimatum, as you are doing that. The best thing you can do is acknowledge just that, so it's not construed as a manipulative ploy.
Acknowledging his perspective and feelings about this decision, while conveying yours. Show him that you understand that it will be difficult for him. If he's still determined to take it that way, after your best efforts, there's not much you can do.
If I appear too accusing, maybe he'll think, "If I agree now, will
this become a recurring behavior she uses every time we disagree about
This is something that may pop into his head and these are things that are difficult to navigate, as his fears can only really be allayed with time and experience, that it indeed hasn't happened again. This is where relationships take time to develop trust to for people to feel comfortable to explore the possibilities of a future together.
Advice moving forward
Do not have sex with anyone unless you really want to, whether it is with this person or anyone else. That is your basic right.