Even if it's a rainy day, it is fun to spend time with you.
Spending time with you makes things enjoyable, even if it's raining.
ご質問ありがとうございます。
① "Even if it's a rainy day,"＝「雨の日だとしても、」
"it is fun to spend time with you."＝「あなたと時間を過ごすのは楽しい。」
② "Spending time with you makes things enjoyable,"＝「あなたと一緒に時間を過ごすと楽しい」
"even if it's raining."＝「雨が降っていても。」
ご参考までに。
Even rainy days are fun, as long as I am with you.
「雨の日もあなたと一緒なら楽しいね」
- Even rainy days are fun, as long as I am with you.
- As long as I am with you, even rainy days are enjoyable.
- Even on rainy days, I feel happy as long as I am with you.
- Rainy days are lovely as long as we are together.
アメリカ合衆国 
