Husband not able to have . I'm considering an open marriage - how do I gain my husband's approval?

Since our marriage over 4 years ago, our life has gone from sporadic-at-best to completely non-existant. A YEAR has gone by now since we've even tried. He's on anti-depressants, which we think is the problem, and he's asked his dr. but the side-effect can't be avoided (he's tried them all). He doesn't wake up in the morning with what other men have to contend with, is Master of His Domain because he has zero interest, etc. Before we married, the was great, but he got depressed and picked fights - so a "happy & less" is better for us than "good but lots of fights". He's a lovely man, great father, and we have a good family life. But there's something missing - it's like living with my brother. I'm pretty, in fab shape and am 34. I want permission to go outside the marriage (wouldn't be often, maybe 1-2x a year?), but my husband won't hear of it. Are my only options a) be dishonest/cheat, b) no from-age-30-to-death or c) leave happy marriage for lack of sex?