I am just going by what I know, and experience of going through this, but I am quite sure that they could put a single crown on the implant now, and then at the later stage change it. But, the cost of this is going to be quite high. As the crowns themselves are expensive. So assuming you changed it again in a year or two, I would assume you would then need to pay for two crowns (even if they are on one implant) as then it is going to be two new crowns. Unless they can just add one on, but I am not sure if that could do that, as they will need to be fused together iyswim.
How I know re the crown pricing is that I am being treated by two different people. The bone grafts and implants by a specialist surgeon (my case is complex) and then I head on over to the dentist for the crowns. So I have paid separately to surgeon for the groundwork treatment and now to dentist for the rest.
Just also wanted to say, perhaps don't get too focused on that next tooth that is a little lose now. I had the same and we discussed pulling it at the same time, but surgeon said no, to wait and see if it secures itself again. Remember that bone regenerates itself, so at the moment it might be feeling a bit sorry for itself as they have drilled into the bone next to it, to put in that implant. It may very well firm up again. In my case it didn't as my bone loss was too severe (I had a impressively size cyst removed and it left a horrendous hole, way too big to the bone to regenerate itself), so after waiting 4 months to give it a chance, it was clear that tooth was dying as it had no bone to support it. So out it came and an other implant went next to it, and that tooth will be covered with a bridge. But, he didn't just whip it out, he said it needed to be given a chance before that decision was made.
You didn't say how long ago you had the implant placed, so if it was recent you will need to wait some months for it to integrate anyway. Maybe by that time, Wobbly might have stopped playing silly buggers.
Also, its not vanity to want your teeth to look okay and to be able to smile and face the world. I feel exactly the same as you, this knocked my confidence and self-esteem that I thought no-one else would understand. I am also single, and never while I have dentures would I consider attempting to meet up with someone new. I was doing online dating and going out to meet new people before this all started, and that was first thing that was stopped in its tracks. I do not want to know or even hear about meeting someone right now, as I am too ashamed about it. I lost 5 teeth and have had four implants placed. One failed implant and one failed bone graft. So I have been through the mill, so I do understand exactly how you feel. It is a slow process though, and so what I will say is, hang in there.