It's not an uncommon practice for a guy and girl friend pair to create a "just in case/one day" plan. A pinky-swear promise of sorts that states that if both parties strike out in love by age X, they'll get get married, or make a baby, or get a house or just get old and fat together. It's sort of like a "best case scenario in a worst case scenario" promise that some like to tuck in their mental back pocket in case life doesn't go as planned.
Is it a serious offer? Probably not, but it offers the individuals involved some emotional assurance that while sailing the seas of dating, a life vest of sperm or hugs will always be out there -- a voucher you won't drown like an anonymous stone into the pit of lonerdom.
But what makes your scenario different (and insane) is that a guy offered you "the plan" while still dating you. He didn't offer this from the vantage point of a dear old friend interested in creating a mutual plan; rather, a boyfriend who saw no future with you, but could foresee throwing you some bone(rs) if need be. You had a right back then and still have a right today to feel like 'WTF is up with that?'.
My advice is: continue seeking other means to achieve your "one day" goals. Even if your scheduled "one day" is this year. You're better off pushing back your time-line than pushing yourself to redeem this dudes DNA voucher. This is some "just in case" sperm that doesn't swim right.
I have an ex who I have the same plan with. I know, kind of dumd, but I wont always be young, cute and desirable to men. One day, I'll be an old hag. And if I havent settled down or had children, he would be the best choice at that point. He isn't a bad guy, and we only broke up because of a long distance issue. We both date and have had boyfriends/girlfriends since then. I think it's more of an insurance thing, instead of something literal. I doubt we will run to the alter and try and conceive on my 35th birthday.
I know someone who did this....for real at age 40 just because they wanted a baby and the clock was ticking. And all I can say is life long friends does not a spouse make. Now there is a gorgeous child with parents who aren't in love with each other but won't leave because of her. Sad.