I consider tact to be about what topics one brings up and in certain decisions about how to phrase a truth. If you're talking about X, you can say all and only true things about X without being unnecessarily rude. If you're not already talking about X (or doing something that implicitly makes X the topic), and it's not something that's polite to bring up, there is no need to express truths about it; that isn't dishonesty, that's being appropriately topical.

If I were under a mistaken impression about a significant other's enjoyment of shopping (not that this would be likely to come up, since I don't care for shopping myself), that would be to no one's benefit. in a distant possible world where I go out and buy things recreationally, I would prefer to do so with people who actually share that interest and trust me enough to believe me when I say I want honesty. I am not a friendless loner; people who are friendless loners probably should look into that before they start hunting for romantic relationships anyway. If my significant other lied to me and said (s)he liked shopping, I'd take him/her along and be missing out on an opportunity to go shopping with someone who genuinely liked it instead.