I think you need to consider whether having their father around will enhance your kids life. Kids need good routines, kindness and caring. If their father isn’t a good person, they are better off without him. If he is fun, gets involved, they have regular times together etc. There is no reason to cut him out. They may grow resentful if they lose out on having him around.
Many parents make the mistake of thinking any dad is better than no dad, but don’t get bogged down in worrying about future issues. Parents make mistakes, and you can’t predict the future. We can only do what we feel is right at the time, and as your kids grow, they will understand that you made the decision with their best interests in mind.
Your love is what they need, and protection from anyone who could cause them harm.
It is hard on kids, and avoiding abandonment issues is important, but inconsistent behaviour and lack of birthday cards etc. can be more upsetting.
Growing up with one parent is tough. Reminders on Father’s Day, who gives you away at a wedding, growing up seeing a functional relationship etc. equally seeing a dysfunctional relationship won’t help either.
The fact that you are seriously considering what is best for them shows how much you care. They will be fine and you are enough. It’s sad when things don’t work out, but know that you can raise wonderful, well adjusted children as a single parent.