I think your ex-boyfriend is just a lousy guy, plain and simple, and you should not be encouraging him in any way or even be scared of him. Talk about what he is doing to someone you trust totally, and someone who can guide you as to the best course of action. You could register a complaint with the police, if possible, of harassment, and make sure they officially direct him to stay away from you. You said he is engaged. You should also make it a point to ensure that the police tell his fiancée about what he has been up to, so she knows what kind of a guy she is planning to get hitched to.
I think the best thing for you is to tell him off, to stay away from you, inform the authorities if you think things are serious enough, and also inform his fiancée. He is just trying to take advantage of the fact that you are a woman, and probably thinks you have no one to turn to. Show him you are wrong, and move on with your life.
BOUNDARIES...SET SOME BOUNDARIES! He is your ex no more sex! Spying on you? That is stalking. There are laws against stalking. GET A RESTRAINING ORDER AGAINST HIM. He sounds a little out of control and possibly dangerous. Call the police if necessary. Do not allow him to intimidate you. I went through this w/my ex. Thank God I lived in a secure building.
Krissy, that is absolutely dangerous. I would suggest that you tell someone close to you about him. We never know when guys like him might act and do something dangerous. So keep everyone alerted. If it becomes really serious, do lodge a police report.
Otherwise, just tell him that you do not want such no-strings-attached relationship. It is not proper for you, as it's only going to bring pain and regret to you later when he gets married. Also if you do not solve this before he gets married, it is going to spell trouble for his marriage too. Do think about the future of the bride as well. Let him know that you want nothing to do with him, and certainly not sex.
Just remember Krissy, don't stoop so low for this guy. It's not worth it. There are lots of better guys out there who will be able to give you love, care and definitely a better sex life.
You need to go to the police. If he knows what you are doing all the time, this means that HE IS STALKING YOU!! This is illegal!!!! You can probably get a restraining order, and in it, it will probably state that he is not to contact you directly or indirectly, and may not come within say 1,000 ft. of you. You could tell his fiancée, but the odds are that she will not believe you, she will be more inclined to believe the man that she is going to marry.
Get pictures of him watching you if you can, to show to the police that you aren't a nut, and that he is actually doing this. Let people you know about this, and let them know at work if you work, show his picture around at work also, as he may try to show up there. This way if the need arises, security can be informed, and he will be removed from the premises.
This way they will know that he might be a possible threat. Someone with a stalking personality can be a very dangerous person. They think that they have every right to be doing this, and odds are that they think you are still theirs. It can escalate, and become life threatening, so go to the police, and get to the court and get a restraining order as soon as you can. Be safe.
I think he wants do it with you because he wants some experience before he does it with his so-called wife. Guys are known to do this quite often. You can tell him to back off or you will have to inform about this to his to be fiancée
I don't think you should be involving police at all They can create a mess unnecessarily in your life.