Well dear, affairs of the heart are something that we really don't always have the answer for, until we look at it from decades away.
Yes, I do sympathize with you. For the most part, we each need that one special person in our lives and, it is the Very Rare individual who is fortunate enough to know, the instant they lay eyes on someone, that "he is The One."
As I read you post, certain points stood out to me.
1) He's nice.. 2) He's good looking.. 3) Successful.. 4) You have a good time with him.. 5) He wouldn't hurt you... 6) You're not as attracted as you used to be.. 7) You Should Be totally in love..
When I "analyze," those statements, I see nothing about how you Feel about him, nor do I see anything about how he is in love with you. I do not see the kind of attraction that keeps a husband and wife together forever, no matter what life throws at them.
Gretchen, there are a lot of "cutsie," sayings about what love is or does.. one being, "Love is never having to say, 'I'm sorry.'"
Bunk. Love humbles itself and, is hurt when others hurt. Love says, "I value you, respect you and cherish you For Who You Are and... what can I Do For You...?" Real love does not say, "what can you do for me?"
Love puts the other person first, always. And, when you have two people who go thru life that way, always putting the other one first, you will have mutual respect and bond that grows naturally and effortlessly to stand against all odds.
Love endures long and is kind; love does not envy the other person and love isn't proud... Love doesn't intentionally hurt the other person; you can't do that if you are apply all that I suggested in the last three paragraphs.
And, love is not based on physical attraction, though that is what normally draws us to someone. At my age, I will testify that what you were at 20 all seems to find its way to your ankles at 60 and, that's when you see the person for who they are inside, and love That, not the physical beauty.. My husband still calls me his "bride," even though I look like Mrs. Haversham... But, he doesn't see that; he sees Me.. who I am in my heart.
True Love grows out of respect, committment and patience. When those things are there, it is a wonderful thing.
And, as a last note, when the ex-boyfriend shows interest, it strokes our ego. We are still desireable. Not to say that he is not the one (you will have to work to find out) but, that is one very real factor in our response to the situation.
Whatever you do Gretchen, Be Sure.. Once the feathers are all out of the pillow, and blown down the road by the breeze, we can never put them all back in.