I fully agree with not disclosing this on your dating profile and not mentioning it on the first date. Except if you were to follow @Thisiswhatyoudo's advice to switch to specific online herpes dating sites. This might take away some of the stress that goes with "hiding" it at first. I'll be assuming you don't do that for the rest of this answer.
Let's say that the first date went well and you're both still interested in seeing each other more. Your current approach is to then send a text to inform your potential partner about your disease.
- no false hope for your partner (a good relationship starts with trust)
- gives them an easy out
- they might not know about it and don't bother to look it up.
- may opt out too soon because of it.
- you can't see how they react to it.
Both the good and bad thing about texting it is that it's less personal. Since you seem to be having some trouble actually finding a partner that sticks, you might want to gently push them a bit more. I suggest to do the following instead of a text message.
Invite them on a second date. Make sure to do something where they are not "trapped" (like in a dinner date, unless if you tell them only near the end) and preferably have some privacy (you don't want 20 other people listening in on you talking about a disease probably).
Some suggestions for such a date could be as simple as going for a coffee (in a non-crowde place ofcourse), walking on the beach, maybe even going to a movie and stick around to have your talk afterwards ...
Then at some point prepare yourself to have "the talk". It starts basically the same way you do via text currently. Be prepared for 3 major possible reactions:
You can't help it. Some people just are disgusted by any diseases. At this point just be glad that you found out early that you're most likely not a good fit for each other (which is what dating is for right?). It's the main reason to go for a date where they can actually get out if they want. They may get over their initial automatic reaction of disgust and contact you again which can give you the same result as the other reaction. Just stay friendly, allow them their out and move on. You expected this could happen in the first place.
2) confusion (what I expect the most probable respons)
This could still work out if you play it right. You're probably going into a "gentle teaching" mode here. Allow them to ask questions about what it is or what to expect to happen later in the relationship. Be open about it. You can be proud that you're showing enough trust in them to share your "secret". You may even want to emphasise it when you do your initial explanation that you want to start of any potential relationship based on honesty.
If they really want out, just let them. Otherwise allow them to think about it, stay in touch (through texts etc...). You should be able to get a decent idea about whether or not they're still interested after this date. Be it in how they respond, or their general body language. Do note that being a bit more distant after your explanation is normal. Give them some time and who knows they might still be interested afterwards.
3) perfectly normal.
Not as likely as the other responses but there are always people who are open about it. Perhaps they have experience with it, or have HSV1 themselves which puts them at ease that they're not alone. They may still have some questions about it but the conversation should flow a lot easier than in case (2). It could be a good idea to show them how glad you are that they appreciate your honesty here.
To end I would like to point out that this approach could be too hard on you as well. You need to be able to muster up the courage to actually tell them face to face. If you're not able to do so than your current approach of texting may still be the best. If you do try it however, don't get discouraged when the first tries end up in situation (1). Keep it up and let's hope you will someday find the one for you.