Does increase in one company's outstanding shares decrease the value of my stock?

Usually, comparing "forward" "earnings per share" with "diluted earnings per share" should give you an idea as to whether a change in number of shareholders may influence the value of your shares.

There are different reasons for the number of shares to go up (or down). As Flux commented, depending on why the number of shares changes, you might have different expectations for whether the earnings per share might change.

Many companies expect possible obligations to issue shares for some reason - for instance, debt holders may have the right to convert the debt to stock. This would dilute your earnings as a shareholder.

The company could also raise capital by increasing the number of shares through a secondary offering (like an IPO, but for a company that's already listed). In theory, if they invest in growing the company, earnings should grow in proportion with the cash from selling new shares, and your own returns would be the same.

Another possibility is a buyback, where the number of outstanding shares decreases. In this case the company pays investors to sell their shares back to the company. You could hold your shares and expect their value to increase, since the same earnings would be distributed among fewer shareholders.

You would have to evaluate what the reason for the change in the number of shares implies for the profitability of the company. For instance, convertible debt could mean lower interest expenses.