[2022] Someone boosted me without my knowledge and I feel awful

I was playing 2v2 recently and was playing my Grand Champ rank up match where my teammate threw. I then lost the next 3 or 4 matches in a row. I was frustrated and wanted to make sure my teammate tried hard in the upcoming match so before the match started, I told them that If we won the match, I would buy them a pizza. We ended up winning and they wanted to party up after so I did. I told them that if them and I managed to get to GC without losing twice in a row, I'd get them pizza for a week. We ended up getting to GC and getting the rewards. I even looked at their stats online afterwards to ensure they weren't on a second account or anything but the number of games played and rank history implied there wasn't anything too suspicious going on.

I did get them the pizza and in the process found out that they had been on their friends account who paid them to get the rewards. I was immediately crushed when I found this out. I tried so hard to ensure that I got to GC without extra help only for it to go down the drain.

Should I have promised pizza? Probably not. I don't know whether this is against the rules since I didn't offer the pizza for them to boost me. I offered it as a kind gesture to a friendly teammate who would work with me to achieve my goal. In my eyes, the offer was to another C3 player wanting to hit GC as well, not a smurf.

The smurf was good but not insanely good or even much higher than myself so I had just assumed they had either gotten a bad streak of losses or needed a teammate to play with.

This has been killing me and need some community input. On one hand, I feel like I didn't truly earn the rank. On the other hand, I had no clue the person was a smurf when I teamed up with them to get to GC. Had I known, I wouldn't have played with them.