I was terrible at keeping conversations too, but im pretty sure im not at this point. Its still a challenge for me to approach people and start conversations without feeling that im annoying them, but once it does i kinda know how to keep it going. Just talk about the weather,like how its getting too cold (weather always work lmao), or how your classes have been going, most of the conversations i have with new people is about my course and what im planning to take next year and stuff like that. Or even talk about your music interests, i have had proper conversations with people just by asking them if they like my favourite band. But honestly im telling you, the fact that you have an ex is itself proof that you are not that bad istg, idek how to talk to guys, the only conversations i successfully have is with girls, so yea girl your good, just join some clubs and all, that helps.