1) A man's height has NO IMPACT on his penis size, the shortest man I've been with was 5'5" and his penis was over 9 inches; the tallest was 6'7" and his penis was maybe 6 inches
2) Her ex's penis size doesn't matter, it really doesn't. I've been with 4 men with extremely large penises and my husband knows this. My husband is well hung, but nowhere near as huge as some of the men I've been with. I don't care. My husband is the best lover I've ever been with and that's what matters. Besides, I never liked monster-cocks, they're simply too painful for me.
Get over thinking about her ex, he's her ex for a reason. Respect the fact that she chose to be with you.