You may need to figure out why your relationships don't last.
The guys might be very different but their may be a common factor in your choices which hasn't been obvious.
Or you might have fears on commitment, losing yourself, being smothered, contoled, betrayed or abandoned.
Or you might have difficulties in communication, conflict resolution and/or boundaries.
Once you know the cause, you'll be able to start finding the solutions.

That's what my dad did. He waited till he was 40 years old to start having kids. I was the first born. My mom was 31 when I was born. My dad was 40.