Thank you for the request.
It sounds like there is possibly a sexual issue that you are dealing with or you are fearful of being close to others, especially sexually. If you feel ok being in a relationship and even kissing them the first few times, then you are able to start relationships through connecting and relating. But if after a while you are unable to continue with them and break it off, there is something that occurs that changes how you feel at that certain time in the relationship. Finding out what changes for you can help.
You may want to try either talking it out or writing about what occurs for you when you find yourself changing from being attracted to these guys to being so turned off that you break the relationship apart. Some of the possibilities are fear of getting too close, anger at them or at yourself and past abuse. You could be fearful of having sex because it is too intimate for you and reminds you of past abuse or a past trauma so you distance yourself, still maintaining the connection but keeping your distance physically. If you experienced hurt from another partner while you were sleeping
with him, that is another possible reason. Whatever is causing it, your mind has somehow connected sex with a partner with disgust or even self preservation so you are not hurt again.
Discovering what might be causing this may take some digging. You need to explore your past for any possible unresolved issues that might be causing this. Write down the feelings you have about your relationship and talk to your therapist about how it relates to anything in your past. You can also learn more about relationships and what causes feelings like you have. By learning more, it can give you ideas of why you might be sabotaging your relationships. Here are some resources to help:
He's Scared, She's Scared: Understanding the Hidden Fears That Sabotage Your Relationships by XXXXX XXXXX and Julia Sokol
Being in Love: How to Love with Awareness and Relate Without Fear by Osho