Well, you didn't specifically say you were getting married, but you did say that this seems to be in connection with you realizing that it might go long term.

It seems like you've got anxiety related to commitment. Probably something you should see a therapist about. You also seem to be projecting your ex coming out as gay onto yourself. Again, something to talk to a therapist about.

Overall, there's nothing "wrong" with you, but some time with a therapist may help you work through what's going on.