I would ask a heap more questions in relation to your question and I know that is really irritating. I have to know in order to answer this --
1. Why did you choose to have two lovers in the first place?
I don't understand because, even my crushes for the most part have been monogomous... well the crushes I encouraged myself in.
2. What attracted you to them?
3. What do you want out of a relationship?
4. What do they want out of a relationship?
5. What is now making you ask this question -- as somebody has pointed out why can't you continue having your cake and eating it too?
6. Sex clouds your judgement a lot.... (that is a statement I know) is this part of the reason that it is difficult to decide?
(be honest with yourself)
7. How do you choose between two lovers?
Me personally, I wouldn't have two lovers.
I would want to give the one I am with the best possible chance of showing me thier love for me in a whole hearted fashion, so I would not put myself in this predicament...
I would not like to be compared against the girl in the afternoon, a distant memory is much easier to beat.
In other words, I would not like to find that the person I am with has another that they are with..... I would not like that at all.
I hope that is helpful.