My BF is nice to my kid because he knows I would not date with him if he does not like my kid.
Do not trust relationship too much. I have a neigbour who had been dating with his girlfriend for 3 years and finally they broke up (Most likely because the guy does not want to marry again). Another neigbour changes his girlfriend once a year. But all of these people, they never and will change their children and they love their children much more than their partners.
You can email me if there is anything I can help.
Take good care of you and your son! You are the one who can give him happiness, but you can also be the one who can ruin his future if you make a wrong decision.