Hi Aly.
I've had to delete the quote you posted from another website because copying content from other websites violates copyright laws.
However, I do agree that dreaming about an ex could be a way of reminding you of similarities between that relationship and the one you have now, and warning you not to get into bad habits that you got into in your previous relationship.
Since you are at the 3 1/2 year mark in your relationship now, you are getting to the point in your relationship where you are started to feel "settled", so you could possibly be worried about slipping into habits that could cause problems.
On the other hand, the dream might not have anything to do with your ex or your relationship with your ex at all - it could have to do with the time during which that relationship took place. Maybe something was going on then that reminds you of something that is happening in your life now, which may or may not have anything to do directly with either your ex or your current boyfriend.
There is some information on this page on
Relationship Dreams that you might find helpful.
Also, if the dreams about your ex mainly involved having sex, then your dreams could just be a normal release of sexual urges. It's pretty normal to have dreams about sex with people other than your partner. It doesn't mean that you would actually have sex with them.
If you love your boyfriend and are happy in your current relationship, you shouldn't do anything that might hurt that relationship.
You should definitely not feel guilty about dreaming about your ex. It's not something that you can really control (unless you are lucid dreaming, which is a whole different story).