Upload & Sell: Off
To directly address the OP's situation, it's important to consider the following points:
1. The lens is a GIFT. Thus, the question of whether the lens is worth the money is not of much importance (i.e., "do I need the money?" is not relevant). Rather, the decision should be placed in the context of whether something else could be more useful to the OP at the same price point.
2. The OP is using an APS-C body.
Personally, if I were in your shoes, I would trade the 85L for other lenses. As nice as it is, I fully accept that it's a demanding lens to use, sub-optimal for APS-C bodies, and the vast majority of photographers really should use the money to buy something that would serve their overall needs better. The unavoidable fact is that the 85L is a specialist lens, and it is meant to take a very specific type of photograph--the low-contrast, low-light portrait shot with maximum background blur. Yes, you certainly *could* use it for other things; but other lenses would be just as competent if not superior for these other shots.
I believe there are very few photographers out there who actually need this lens, in the sense that the purpose for which it was designed is so important to them that the $1500+ premium they'd pay for it could not be better utilized to meet their other photographic needs. It's not about the cost itself--e.g., there are plenty of wealthy amateurs out there who buy the 85L, but should have spent the money to buy an 85/1.8 + 24/1.4L II because they don't have a fast wide-angle prime and would get more use out of one. Or they could spend it on a 135/2L, or a 100/2.8L macro IS, or a 24-70/2.8L, or... Do you see my point? It's not necessarily that the lenses cost what they do; it's that for the money you spend, you want to maximize the benefit of what you spend. If you are missing certain types of lenses that your style of photography could utilize, it makes more sense to put the money toward those. If the specific benefits of the 85L are included in that calculation, then that's when you look to own one.
And yes, I own the 85/1.2L II, and I used to own the 85/1.8. But I don't use an APS-C body.