The boss is suspicious

I haven’t been in this situation before so I’m bound to fuck up soon, My long time readers will know that I haven’t worked anywhere before I came to the plant(ation) and as a results I haven’t been in a situation were by you have to look for a new job. I took leave on Friday so I came back to the torture chambers this morning, I wasn’t job hunting or anything like that but I had a few items I had to return to the campus library on Monday and on Tuesday I had lunch with an old flame so I really couldn’t come to work. I gave the secretary leave forms and he knew that I would be absent from work for two days, I didn’t personally give him the leave forms because he was at a meeting. I thought everything was fine, I enjoyed my two days leave, I relaxed and drank a whole lot of Rooibos tea.
I came to work this morning and I found out that my boss had spend the whole two days trying to find out what I was doing these past two days, he asked two of my colleagues where I was. This is strange because he must’ve saw the leave form and he probably knew i had taken leave. i think he wanted to know what I was doing during my two day break, earlier during the week I had told a the project engineer that I was planning to leave the company and I think she told him. I’ve applied for three jobs and I might have Interviews lined up so how do I keep that from my boss he’s very nosy and I don’t want him to know that I’m serious about leaving I want to surprise him with a letter of resignation which reads “Fuck you for wasting six months of my time”.