How do I (30F) stop the short term relationship cycle and create safe boundaries?

I have met some guys through OLD who I’ve gotten pretty deeply involved with. At least 3 men in the last 10 months. I’ve genuinely liked and cared for them in their own ways. Now, let me preface again, that I’ve been blocked by all three men. Obviously, none of them worked out and I’ve felt pretty heartbroken about it. Almost, becoming a little bit more cynical about dating each time. Having casual sex is just too difficult for me as I catch feelings pretty easily. I am genuinely someone that can find the good in anyone, and have made far more than it is worth efforts with men who I just don’t click very well with.

I am just wondering, how do I create more safe boundaries for myself so I will not get too attached before I am sure that they really want me too? It seems like they want me to care for them, until they don’t. I sometimes just like not getting to know anything about them until we have been on a date or two. I know the commitment and attachment can be a real turn off but it seems like that is what these men want but they also don’t.

I just feel so tired of investing in someone who flips the switch 3 months in and doesn’t want anything to do with me! I want to create steps for myself, so that I can guard my softness and care that should be saved for someone who can reciprocate the same thing.