How do I deal with low self-esteem?

So I'm 21 and I haven't been a "skinny" girl in a very long time due to a range of issues including an unhealthy lifestyle, depression, birth control etc but recently (about 6 months ago) I started taking an SSRI and my weight has exploded out of control. I look and feel terrible, most of my cute clothes don't fit anymore and I'm starting to have a hard time just getting from one place to another. It's awful. Despite all of this, however, I am in a great relationship of around a year and a half with a great guy. He's very lean and fit and has a history of athleticism; however, his depression has decreased his motivation to exercise ... and his sex drive :/ I can't keep myself sometimes from voicing my frustrations related to my weight to him, and I know that it frustrates him to watch me eat badly and not exercise when he can tell I'm so upset about how I look these days. On top of that I can't help but feel like he finds me much less attractive now than he used to, now that I'm a depressed blob all the time (I stopped taking the SSRI a few weeks ago). We used to have such amazing sex and we haven't had sex in weeks despite all my attempts to initiate :/ I know that his depression is the biggest factor in that but I feel like he's also less interested in seeing me naked :/ He tells me what draws him to me the most is my "confidence," and as a point of reference keeps bringing up the summer we first started dating, when I had a very active job and lost a lot of weight, only to gain it back again. I know I need to do something about my lifestyle, and I have an appointment with my psychiatrist to talk about a different SSRI so I don't have to choose between my emotional state and my appearance, but in the meantime I just want to feel like myself again. I hate the idea that my weight is affecting my relationship, because it never has before with anyone I've dated. How do I deal with this? What can I do?