Well obviously no-one else here apart from you actually knows the guy but it really seems to me from what you have posted that he wants to be monogamous and that is what would make him happy.
Yes he is consenting to this situation of you sleeping with someone else, but my whole point before was that due to the fact that he is in love with you and does not want to lose you/is a nice guy and wants to make you happy, that the consent is not really worth that much. If he loved you less he would leave you. And just because he loves you enough to stick around doesn't mean he doesnt feel shit inside.
And to the two people that have suggested that I have a problem with Aurelie because she enjoys sex you are wrong. Nowhere have I said I would have a problem with her enjoying all the sex that she wants if her sex life didn't centrally revolve around a romantic relationship with a unbalanced to the point of exploitative power dynamic.
Polyamory is something for equal partners to participate in together and to pursue because its what they want and enjoy, not something that someone has to suffer and accept because they are in love with someone who won't stop sleeping with someone else.
Honestly if the most important thing for you is your boyfriend it would be prudent to break up with your lover, because I don't see this situation being sutainable, the longer this situation carries on probably the more the resentment/pain will build up under the surface. If your not that fussed about him stick with the lover, dump the bf to be kind and find some people to be poly with that aren't reluctant and suffering for it.